There is relatively little research on the relationships between adults with intellectual disability and their siblings, despite the potential importance of these relationships for either individual's psychological well-being and future care roles that might be adopted by adult siblings. In the present study, sibling relationships of adults with adult siblings with (N = 63) and without (N = 123) intellectual disability were explored. Contact, warmth, conflict, and rivalry were measured using questionnaires available as an on-line survey. Expressed emotion was measured using the Five Minute Speech Sample over the telephone to establish an independently coded measure of criticism from the participant towards their sibling. Overall, there were few group differences in contact and sibling relationship. There was less telephone contact in the intellectual disability group, and less reported warmth in the relationship with siblings with intellectual disability although this was mainly associated with severe/profound intellectual disability. Exploratory analyses were conducted of the correlates of sibling relationships in both the intellectual disability and control groups. These analyses revealed a small number of different associations especially for conflict, which was lower when either the participant or sibling was younger in the control group but associated with relative age in the intellectual disability group.
The most long-lasting and enduring relationship an individual develops during the lifespan is the sibling relationship (Cicirelli, 1982). The literature on adult sibling relationships has mainly focused on two fields of enquiry. The first is on factors relating to the quality of sibling relationships including gender, birth order, family size, and age differences between siblings (Dolgin and Lindsay, 1999, Lee, 1990, Newman, 1991, Pulakos, 1987 and Pulakos, 1990). For example, research by Dolgin and Lindsay (1999) on disclosure between college students and their siblings, revealed that later-born siblings disclosed more to their siblings than earlier-born siblings. Siblings from smaller families have been shown to communicate more than those from larger families (Newman, 1991), and sibling relationships of females have been found to be more intimate than those of males (Dolgin and Lindsay, 1999 and Pulakos, 1987).
The second field of enquiry has addressed the functions and features associated with adult sibling relationships (Dolgin and Lindsay, 1999, Riggio, 2000, Stewart et al., 2001 and Stocker et al., 1997), frequency of contact (White & Riedmann, 1992), and the importance of sibling relationships compared to other close relationships (Cicirelli, 1980, Floyd, 1995 and Pulakos, 1989). Stocker et al. (1997) identified three dimensions of adult sibling relationships using factor analysis methods: warmth, conflict, and rivalry. White and Riedmann (1992) demonstrated that 50% of their sample of 7730 adults reported seeing or talking to their sibling at least once a month and that genetic closeness affected emotional closeness among siblings. In contrast, Lee (1990) demonstrated that geographic proximity, emotional closeness, and feeling responsible for a sibling's welfare primarily explained the motivation to make contact among siblings. Findings on the closeness between adult siblings are also mixed: Pulakos (1989) showed that adults feel closer to their friends, whereas Floyd (1995) failed to find any differences in closeness between friends and siblings. The life transitional events of divorce, loss of family members, and becoming a parent, have been associated with stronger emotional bonds among adult siblings (Connidis, 1992).
